Based on my experience with LLM and developers I personally know, my only assumption is they don't have the skills in the first place...

In corporate world there are a lot of "developers" that actually act kind of like codegen. They just throw plausible sounding bullshit into an editor and hope for the best. Two examples:

Once asked to help a team speed something that ran slow, even by their low standards. Turned out they had made their own copy file routine instead of using the standard library one, and sucked the file into memory, expanding array 512 bytes at a time, and then wrote it out, 512 bytes at a time. I made the thing nearly instant by just making it a call to the standard library function to copy a file.

While helping with a separate problem, I noticed their solution for transferring some file with an indeterminate version number in the middle of the file name. It was a huge mess, but the most illustrative line was the line in their Java application declaring a string "ls /path/with/file|grep prefix.*.extension".....

Lots of human slop out there that AI can actually compete with.